Evaluation of genetic diagnosis methods in intellectual disability etiology

Aim: The aim of this study is to evaluate our diagnostic approach to genetic causes which are the most important etiology of intellectual disability patients and the diagnostic methods used. Method: Followed up for cognitive deficiency 328 patients under the age of 18 who were not exposed to environmental factors such as hypoxia and trauma were included in the study. The prenatal-natal-postnatal histories, pedigrees, and the genetic diagnosis method used in which situations were analyzed retrospectively. The obtained data were compared with the data in the current literature. Results: Of the 328 patients followed up, 179 were male (54.5%) and 149 were female (46.5%). Clinically; 7q11.23 deletion in 2 of 7 patients suggestive of Williams-Beuren Syndrome, CGG repeat in 5'UTR region of FMR1 gene in 4 of 48 patients suggesting Fragile X Syndrome, more than 200 CGG repeats in 5'UTR region of FMR1 gene, MECP2 gene mutation in 5 of 19 patients with Rett Syndrome, Prader Willi-Angelman In 8 of 67 patients with suspected syndrome, 15q11.2 deletion was detected. In the Array CGH study conducted on 309 patients who could not be diagnosed with these tests and whose clinic did not suggest these diseases, a change explaining the clinic of 50 patients was found. A whole exome sequencing (WES) study was performed on 101 patients who could not be diagnosed with other tests and who were continuing their follow-up. Mutation explaining the patient's clinic was detected in 34 of the patients studied with WES. Conclusion: This study demonstrates the comparison of the current literature with which genetic diagnosis test is applied to patients who are followed up with a diagnosis of cognitive deficiency and the success of the diagnostic methods applied. Genome-wide methods such as array CGH and WES provide a high benefit in diagnosis in revealing the etiology of cognitive deficiency with high genotype-phenotype heterogeneity. Application of these diagnostic methods in patients who do not have a specific clinic; By revealing the etiology as soon as possible, it can direct the treatment of the patient, provide the opportunity to reduce the complications that may arise, the material-spiritual impact on the patient and his environment can be minimized, and will pave the way for the family to have healthy children in the next period. Key words: intellectual disability, Etiology, Diagnostic Methods, array CGH, WES